The present invention relates to electrical beverage making appliances and in particular, but not exclusively to electric coffee makers.
A known type of coffee maker beverage type is known which comprises two chambers: a first chamber for receiving water to be heated; and a second chamber which is seated on top of the first chamber and which receives the coffee grounds. The second chamber is in fluid communication with the first chamber through a water transfer pipe which extends down from the second chamber into the first chamber. A separator arranged at the top of the water transfer tube allows water to flow into and out of the upper chamber while retaining the coffee grounds. In use, the liquid in the first chamber is heated externally, for example by a gas or spirit flame or an electric element arranged under the chamber. As water in the first chamber heats, the pressure in that chamber increases causing the water in the first chamber to rise up through the transfer pipe into the second chamber where it infuses with the coffee grounds. Eventually, the level of liquid in the first chamber falls below the bottom of the tube, and transfer of liquid stops. The heating is then discontinued and the first chamber then cools so that steam will begin to condense on the inside of the lower chamber. When it does so, a partial vacuum is created in the first chamber which causes infused beverage to be sucked back down the tube through the separator into the first chamber. When all the beverage has been sucked down into the first chamber, the second chamber can be removed and the beverage be served from the first chamber.
Such an appliance is disclosed in GB 1,332,656. In that appliance, an electric heating element or a gas flame is arranged under the first chamber and controlled by a thermally responsive actuator arranged in the second chamber. The actuator senses the temperature of the atmosphere in the second chamber and when it reaches a predetermined temperature either discontinues the electrical supply to the heating element or operates a valve in the gas supply to the gas flame.
One problem with the above arrangement is that it is difficult and expensive as the actuator is arranged remotely from the heating source which means that connections have to be made between the two. This results in unsightly and unnecessary housings or shrouds being provided in the apparatus and unnecessary expense. A further problem is that the heating of liquid in the first vessel is slow and inefficient and after the sensor has cut off the element considerable amounts of heat continue to flow from the heater into the apparatus.
The present invention seeks to overcome the above problems, and from a first aspect, therefore, provides a beverage maker comprising:
a first chamber;
a second chamber arranged on top of said first chamber;
a tube extending down from said second chamber into said first chamber for transferring liquid between the two chambers; wherein:
the base of said first chamber is provided with electric heating means and thermally responsive control means are provided associated with the said base so as to be responsive to the temperature of the heating means or a section of the base for interrupting the power supply to or reducing the heating output of the heating means.
Thus in accordance with the invention, the base of the first chamber is provided with electrical heating means and power to the heater is interrupted or the heating output thereof substantially reduced in response to the heater or a portion of the base reaching a predetermined temperature. This stops, or at least substantially reduces heating of the liquid in the lower chamber, so as to stop boiling. The first chamber then cools, water begins to condense on the wall of the first chamber and transfer of infused beverage from the second chamber will commence.
This arrangement allows the liquid in the first chamber to be heated efficiently, accurate control to be achieved and obviates the need for unsightly and cumbersome electrical connections between the first and second chambers.
The control means of the invention may be arranged to operate in one of a number of ways. In a first embodiment, the control means is configured and arranged so as to detect when a portion of the base of the first chamber boils dry, which indicates that a predetermined amount of the liquid in the first chamber has been transferred to the second chamber. This condition can easily be detected by a suitable thermal sensor in thermal contact with the base or the heater since in the absence of water which cools the base or heater, the temperature of the base or heater will rise very quickly.
In an arrangement as described above, preferably only a specified portion of the base or heater boils dry, such that water still covers the remainder of the base.
This may be achieved in a number of ways. For example the base or heater may be provided with a locally raised region which boils dry. This region could, for example be formed as a raised region of a heater plate such as is disclosed in Applicant""s GB 2,316,847 to which reference can be made for further detail. A suitable sensor may then be arranged under the raised region which will become exposed in advance of the remainder of the base.
In an alternative arrangement, the base or heater of the first chamber may be generally planar, but arranged to slope such that a peripheral region thereof will become exposed and overheat as the liquid level in the first chamber drops as liquid is transferred to the second chamber. A suitable sensor may be arranged under that part of the base or heater.
Preferably, however, the base is provided with a region which is separated from the remainder of the region by a raised wall. Most preferably, the wall surrounds the entire heated region of the base. This wall forms a reservoir of water above the heater in the base, and it will be appreciated that the higher is this wall, the longer it will take for water within the reservoir to evaporate, and thus for the control to operate. This allows a mechanism by which the beverage infusion time can be varied since that is dependent upon how long the water remains in the second chamber. This is, in turn dependent upon maintaining the pressure in the first chamber, which in turn depends on the continued boiling of liquid in the first chamber. Thus in a preferred embodiment, the wall is adjustable in height to allow for adjustment of the beverage infusion time.
A further way in which the infusion time can be varied is by varying the power of the heating element. If the element is heats at low power, then it will take longer for the liquid in the reservoir to boil away, thereby maintaining the vapour pressure in the first chamber for a longer period, thereby keeping the hot water in the second chamber infusing for a longer period of time. Conversely, if the element heats at high power, then liquid in the reservoir will boil away more quickly, thereby reducing the infusion time. In one embodiment of the invention therefore, means may be provided for varying the power of the heating element. Means for achieving such a power variation will be readily conceivable by the skilled person and are thus not described in further detail here.
A yet further way in which the infusion time could be varied would be to have an additional heater which heats a portion of the base which would still be covered by water after the main heating element has been switched off. This element need not be particularly high power, say 50 W, but even at that low power it would generate sufficient vapour to maintain the vapour pressure in the first chamber. The additional heater could be switched off after a predetermined time to bring the infusion period to an end.
In the embodiments described above, the temperature of the base or heater can be sensed in any convenient manner. Preferably, however, the temperature is sensed using a thermomechanical sensor such as a bimetallic actuator arranged in good thermal contact with the base or heater. In the preferred embodiment, a pair of actuators most preferably operable at substantially same temperature can be employed to sense the overheating condition.
A suitable control of this type is disclosed in Applicant""s WO95/34187. Such a control is equally suitable for engagement with heaters having sheathed elements or with thick film heaters.
A possible disadvantage with the above control arrangement is that with repeated boiling dry of an area of the lower chamber base, scale may be deposited on the base, which would be unsightly. In an alternative arrangement, therefore, the control means is configured and arranged to sense boiling of the liquid in the first chamber via a portion of the base of the vessel. This can be done by sensing the localized boiling dry of a section of the heater, for example by using a system as disclosed in GB 2,283,155. Preferably, however, boiling is sensed by means of a system as disclosed in Applicant""s WO96/01875 and WO98/36616, or in unpublished United Kingdom Patent Application No. 9805751.6 which for the purposes of sufficiency is attached as Appendix I hereto.
In accordance with such systems, a relatively low volume sump will be provided in the heated base of the first chamber, and a thermally sensitive actuator mounted in thermal contact with that sump. When liquid is heating in the first chamber, the temperature of the liquid in the sump lags behind that in the main body of liquid, as there is little convection within the sump. However, when the liquid in the first vessel boils, the liquid in the sump is quickly displaced and the sump temperature quickly rises. This rise in temperature can be sensed by suitable means.
Depending on the boiling time required, the actuator may be mounted in close thermal contact with, or thermally more remote from the sump. If a variable boiling time is required (to vary the infusion timexe2x80x94the longer the boil, the longer liquid will be held ion the second chamber), means can be provided to increase or decrease the length of time it takes the actuator to reach operating temperature. Such means might comprise heat sinks which could selectively be introduced into the thermal path between the sump and the actuator.
A control arrangement of the above type has the additional advantage that the first chamber can be used as a traditional kettle, since it will switch off when boiling is detected, irrespective of the presence or absence of a further chamber. All that is required is that the pouring spout of the first chamber is configured such that it may sealingly receive the second chamber with its depending tube.
This is in itself a novel arrangement, and from a further aspect the invention provides a water heating vessel comprising a water receiving chamber, the base of said chamber being provided with electric heating means, and further comprising thermally responsive control means are associated with the said base for sensing when the water in the chamber is boiling so as to interrupt the power supply to or reduce the heating output of the heating means, said chamber further being provided with a pouring spout which is adapted and arranged sealingly to receive the neck of an infusion receiving chamber.
Preferably, the spout is centred on a vertically extending axis, and preferably is tapered to receive a tapering seal such as a rubber bung. If necessary, a suitable spout cover may be supplied to at least partially close the spout when it is being used as a kettle.
The heating means used in an appliance in accordance with the invention may comprise a sheathed heating element attached to the underside of the base, for example through a heat diffusion plate. Such constructions are well known in the art and so need not be described further here.
In a preferred embodiment, however, the heating means comprises a so-called thick film heater provided on the base. Such heaters are becoming more commonly in the water heating art and comprise a electrically resistive heating track deposited on an insulated substrate. Typically the insulated substrate is provided by an insulating layer laid down on a stainless steel plate. Examples of such heaters are disclosed, for example, in WO 98/36618 and WO96/17496.
The heater may be provided over the whole of, or merely a part of the base of the first chamber. In the preferred embodiment, the heater is formed as a separate unit mounted in a suitable aperture formed in the base of the first chamber.
The heating means of the apparatus may comprise an element which keeps the infused beverage in the first chamber warm after the control of the apparatus has operated. This xe2x80x9ckeep warmxe2x80x9d element may be provided in a number of ways.
In a first arrangement, a keep warm element may be provided which is separate from the main heating element. This keep warm element may be energised the whole time the main heating element is energised or may be switched on only after the control has operated to switch off the main heating element. In an alternative arrangement, the keep warm element may be connected into series with the main heating element after boiling has been sensed. The resistance of the main element (which would typically be an order of magnitude smaller than that of the keep warm element) means that very little heat is generated in the main element part when so connected.
The keep warm element may be arranged to cycle, for example in a manner as described in WO97/04694. In such an arrangement the temperature of the base would be monitored and the keep warm element operated in response to the base temperature. This arrangement is particularly suited to use with sheathed heating elements. However, it has the disadvantage that the temperature of the base may be such as to cause localized boiling of the beverage in the first chamber during the heating bursts, which may be detrimental to the flavour of the beverage.
Preferably, therefore, the keep warm element is energized continuously after operation of the vessel control, but at such a power level that will not cause the beverage in the first chamber to boil. The power required to achieve this can be easily determined empirically by the skilled person. In this case, the element will probably be a thick film type heater whose power level and power density can very easily be tailored to meet particular requirements. Typically, however, one might have a main heating element rated at 1500 W at a Watts density of 50-150 Wcmxe2x88x922 and a keep warm element rated at 50 W at a watts density of 10 Wcmxe2x88x922. A general track arrangement and switching arrangement suitable in principal for achieving such a heating regime is disclosed in GB9805751.6.
It is believed that the above arrangement constitutes an invention in its own right, so from a further aspect the invention provides a beverage maker comprising:
a first chamber;
a second chamber arranged on top of said first chamber;
a tube extending down from said second chamber into said first chamber for transferring liquid between the two chambers; wherein:
the base of said first chamber is provided with electric heating means for keeping infused beverage in the first chamber warm, the heating means being rated such that it will not cause boiling of the infused beverage in the lower chamber.
The lower chamber is preferably configured as a cordless arrangement whereby it my be removably positioned on a power supply stand. This considerably facilitates pouring of the beverage.